If you have a pond with a history of nuisance levels of aquatic plant growth, then the month of March is a great time to begin scouting your pond for aquatic plant growth.
Did you have mats of green hair-like algae floating on your pond last year? If so, that is filamentous algae, which is a common problem in ponds. It begins growing on the bottom of the pond then floats to the surface.
To scout for these algae, use a garden rake and drag it along the bottom of the pond along the shoreline. It will be very bright green, with a slimy appearance. If you find it, the months of April and May are a good time to begin to controlling it.
Monitor the water temperature and begin treatment after it has reached 60 degrees. Unfortunately, algae grow quickly and may reappear later in the summer, but spot applications or partial pond treatments may keep up with its growth if you have reduced the population in the late spring.
Copper sulfate is a contact herbicide used to control algae. Read the label. Copper sulfate can cause burns on your eyes and skin, so read the label and wear the recommended personal protective equipment.
The label also will tell you how much formulation to use based on the size of your pond, and since it is a contact herbicide, it must be dissolved in the water to be effective.
If you don’t know your pond’s size in acres to the nearest tenth of an acre, ask your local Soil and Water Conservation District to calculate the acreage from an aerial photograph.
The aquatic herbicide you purchase may give you several application options, for example, a shoreline banded application rate, and the rate of application per acre-foot of water to treat the entire pond.
To determine how many acre-feet of water your pond contains, multiply the surface acreage times the average depth of your pond. Determining average pond depth requires taking several depth measurements across your pond in a grid, adding the depths recorded and dividing by the number of measurements you took.
You may find other types of aquatic plant life during your scouting trips to the pond. It is very important to identify the plant, as this is the first step in selecting the correct aquatic herbicide to reduce the population.
An Illinois Department of Natural Resources fisheries biologist can help you correctly identify the plant and help with identifying control options. You can find a biologist by visiting: www.ifishillinois.org.
Remember that aquatic plants have an important role in the pond ecosystem. They produce the majority of dissolved oxygen for use by fish and other aquatic animals.
These plants also serve as escape cover for young fish and provide food for some aquatic animals. In ponds without vegetation, pond owners may notice that very few young of the year fish survive because of predation.
As a rule of thumb, a pond supporting a population of fish should have aquatic plants within 20 percent to 40 percent of the pond. Problems can arise when plants become so numerous in a pond that they interfere with fishing, boating, swimming or aesthetics.
Aquatic plant management takes careful thought and planning, so start now. Pond management and aquatic vegetation management publications also are available at the previously mentioned website.